Inverse design of low boom configurations using proper orthogonal decomposition and augmented Burgers equation

Mitigation of sonic boom to an acceptable stage is a key point for the next generation of supersonic transports. Meanwhile, designing a supersonic aircraft with an ideal ground signature is always the focus of research on sonic boom reduction. This paper presents an inverse design approach to optimize the near-field signature of an aircraft, making it close to the shaped ideal ground signature after the propagation in the atmosphere. Using the Proper Orthogonal Decomposition(POD) method, a guessed input of augmented Burgers equation is inversely achieved. By multiple POD iterations, the guessed ground signatures successively approach the target ground signature until the convergence criteria is reached. Finally, the corresponding equivalent area distribution is calculated from the optimal near-field signature through the classical Whitham F-function theory. To validate this method, an optimization example of Lockheed Martin 1021 is demonstrated. The modified configuration has a fully shaped ground signature and achieves a drop of perceived loudness by 7.94 PLdB. This improvement is achieved via shaping the original near-field signature into wiggles and damping it by atmospheric attenuation. At last, a nonphysical ground signature is set as the target to test the robustness of this inverse design method and shows that this method is robust enough for various inputs.     

Pulse Doppler signature of a rotary-wing aircraft

Field measurements of a modified Sikorsky S-55 helicopter target were carried out to investigate rotary-wing aircraft Doppler radar signature phenomenology. The results of the data analysis with regard to classification and identification of the aircraft based on its signature are presented. It was found that using the Doppler radar return and appropriate feature extraction techniques, the helicopter's design features can be estimated. Target backscatter from the main rotor blades, tail rotor blades, or hub can be used for target detection, acquisition, and classification as a rotary-wing aircraft. The extraction of configuration and blade count features can further define the helicopter for identification     

防空导弹攻击目标的红外成像特性分析

通过结合对目标的红外成像特性研究,首先阐述了在复杂背景条件下防空导弹对目标的红外成像寻的制导的组成和原理。然后详细分析了地面杂散背景的辐射和散射特征,综合分析了军用飞机被防空导弹攻击目标的红外辐射特性。在对复杂背景辐射特征和目标红外特性分析的基础上,给出了一组典型地表光谱辐射亮度曲线和太阳对地表的全波段辐射能流(辐照度)随时间的变化曲线;绘制出了红外成像导引头在整个红外波段内的探测效能曲线。分析结果对研究防空导弹红外成像导引头如何从复杂背景中将目标的典型特征信息提取出来并进行有效识别和跟踪奠定了基础。     

A new model to simulate infrared radiation from an aircraft exhaust system

A multi-scale narrow band correlated-k distribution(MSNBCK) model is developed to simulate infrared radiation(IR) from an exhaust system of a typical aircraft engine.In this model,an approximate approach instead of statistically uncorrelated assumption is used to treat overlapping bands in gas mixture.It significantly reduces the requirement for computing power through converting the exponential increase of computing power consumption with the increase of participating gas species to linear increase.Besides,MSNBCK model has a great advantage compared with conventional methods which can estimate each species' contribution to the total gas mixture radiation intensity.Line by line(LBL) results,experimental data and other results in the references are used to evaluate this new model,which demonstrates its advantage in terms of accuracy and computing efficiency.By coupling this model and finite volume method(FVM) into radiative transfer equation(RTE),a comparative study is conducted to simulate IR signature from the exhaust system.The results indicate that wall's IR emission should be considered in both 3-5 μm and8-14 μm bands while gases' IR emission plays an important role only in 3-5 μm band.For plume IR radiation,carbon dioxide's emission is much more significant than that of water vapor in both3-5μm and 8-14 μm bands.Especially in 3-5 μm band,the water vapor's IR signal can even be neglected compared with that of carbon dioxide.     

Wavelet preprocessing for high range resolution radarclassification

We develop a wavelet denoising scheme to aid an automatic target recognition (ATR) system in recognizing aircraft from high range resolution radar (HRR) signatures. A template matching classification technique is used with templates formed from synthetically generated signatures. The goal of the classification system is to achieve classification accuracy equivalent to that obtained with measured HRR signatures. Results suggest that a large portion of HRR signature content is nondiscriminatory. The wavelet denoising process removes the nondiscriminatory information, thereby leading to remarkable increases in classification accuracy. Results are shown for HRR signatures from six aircraft     

New criterion for aircraft susceptibility to infrared guided missiles

This paper assesses aircraft susceptibility from the first principles, with respect to the threat posed by passively guided infrared homing missiles; with an objective of gaining insight into the comprehensiveness of the relationship between aircraft susceptibility and aircraft infrared signature level. The conventional criterion of aircraft susceptibility assessment based on its lock-on envelop is found to be inadequate, and a new criterion termed here as the Lethal Envelop is presented. The proposed susceptibility assessment criterion is more relevant for coming generation of infrared-guided missiles, because of advancements in the infrared detection technology. A threshold infrared signature level is also proposed as benchmark to be satisfied by all infrared signature suppression systems; if aircraft susceptibility to infrared guided missiles is to be reduced. This analysis is vital for gauging the effectiveness of infrared signature suppression systems. A typical air-to-air combat situation is simulated, and the results that lead to aircraft susceptibility assessment are obtained from this model, which illustrates the comprehensiveness of the redefined aircraft susceptibility assessment approach.     

球形离散颗粒抑制尾喷流红外辐射传输数值模拟

以气溶胶烟雾红外抑制技术为背景,以Mie散射理论为基础,利用Fluent软件计算获得气固两相流场,采用射线踪迹法(RTANM)编制红外辐射传输计算程序开展了球形固体微粒环尾喷流喷射抑制喷流红外辐射传输数值模拟研究.研究参数主要考虑颗粒本身的光学特性以及颗粒在喷流射流中的扩散规律对抑制效果的影响.研究表明,各种影响因素中粒径对红外抑制率的影响最为显著,3～5μm范围内粒径在1.0μm左右最佳.      

利用ENSAAP程序计算喷管超音段壁面排气引射冷却系统性能与分析

在基线发动机性能计算的基础上,利用引射喷管抽吸特性和二次流进气系统的流量平衡技术,研究并提出了一种多缝引射喷管方案,用于降低喷管超音段壁面的温度,并开发出多缝引射喷管尺寸与分析程序ENSAAP。利用该计算程序,可分别计算设计条件下和非设计条件下的冷却空气流量和安装多缝引射喷管后所造成的安装推力损失,以及安装多缝引射喷管对发动机重量和飞机航程的影响。本项研究为发展具有低可探测性的先进发动机排气系统提供了可行的冷却方案和设计基础。      

用Tam-Ganesan湍流模型研究排气系统红外辐射特性

通过三维流场、介质的质量浓度场与辐射场耦合求解方法,计算了1台有中心锥的轴对称喷管的空腔-喷流组合红外辐射特性.利用专门为自由剪切流动发展的Tam-Ganesan湍流模型,有效提高排气系统红外辐射模拟精度.采用有限体积法(FVM)结合窄带模型(NBM)计算了排气系统在3~5μm波段的辐射传输问题,并考虑大气衰减作用.对比了采用标准 k - ε 模型和Tam-Ganesan模型对排气系统核心区长度的影响,以及由此引起的排气系统红外辐射特性的变化.通过与试验数据对比证明了该结果的准确性,结果表明选择合适的湍流模型对计算排气系统红外辐射特性有重要的意义.      

典型亚声速飞翼布局无人机红外隐身特性分析

隐身技术作为提高作战生存力的关键环节,是复杂对抗环境下武器装备信息化作战的最重要技术指标。飞翼布局以其独特的隐身优势,成为无人作战飞机首选布局形式。文章以超低RCS亚声速飞翼布局无人机平台为基础,从多频谱隐身特征平衡设计出发,针对其采用低发射率材料前后的红外隐身特性进行了对比分析,验证了红外隐身措施的有效性。     

海天背景舰船红外目标识别技术研究

通过对舰船红外目标特性与识别方法的讨论,给出了图像序列目标识别算法流程以及仿真实验的结果,并对工程实现自动目标识别的硬件、算法和软件设计进行了讨论,具有较好的理论和应用价值。     

红外目标与环境的视景重建技术研究

研究了图像环境生成过程中红外目标特征信息提取所面临的重要技术问题,提出了自适应背景感知与对消处理、抑制背景的自动门限选取和形状分析与目标特征识别的层次化数据处理流程.基于数学形态学理论实现了图像背景感知的应用研究算法.实验测评表明,该算法对复杂变化的图像环境具有良好的滤波性能和稳健的适应能力     

飞行器RCS近场测试技术研究进展与工程应用

雷达散射截面(RCS)测试是隐身技术和目标特性研究的基础。无论是研究物体的电磁散射特性还是研制具有突防能力的隐身武器系统,RCS测试都具有非常重要的意义。通过RCS测试可以验证电磁散射计算的理论和方法,更重要的是,对部分飞行器目标进行电磁散射理论计算非常困难,而通过测试可以直观地获得目标的电磁散射特性数据,从而避开复杂的电磁仿真计算。与外场、紧缩场RCS测试方法相比,近年来得到广泛应用与发展的RCS近场测试方法在飞行器目标的散射特性测试方面具有效率高、成本低的优势。介绍了飞行器RCS测试评估方法,综述了国内外RCS近场测试技术研究的最新进展与工程应用实例,分析展望了飞行器RCS近场测试技术面临的机遇与挑战。     

Dynamic imaging and RCS measurements of aircraft

Results on radar cross section (RCS) measurements and inverse synthetic aperture radar images of a Mooney 231 aircraft using a ground-to-air measurement system (GTAMS) and a KC-135 airplane using an airborne radar are presented. The Mooney 231 flew in a controlled path in both clockwise and counterclockwise orbits, and successively with the gear down, flaps in the take-off position and with the speed brakes up. The data indicates that RCS pattern measurements from both ground-based and airborne radar of flying aircraft are useful and that the inverse synthetic aperture radar (ISAR) images obtained are valuable for signature diagnostics     

基于GRNN算法的飞机用电设备非侵入式负荷监测方法

随着飞机的多电化和全电化,机上电气检测及其负荷管理至关重要,然而飞机上为诊断所设置的传感器数量要求越少越好,非侵入式负荷监测（NILM）方法无需分散进入负荷内部,仅检测汇流条级别电力参数可完成负荷识别。选择稳态电流谐波参数为负荷印记,采集某型飞机交流主汇流条上用电设备真实电流波形,提取1~19次谐波含量建立特征库,用广义回归神经网络（GRNN）算法辨识负荷类别,设置适当样本数和扩展速度以有效提高识别准确度。实验表明：GRNN算法较之BP神经网络算法和SVM算法识别准确度更高,计算速度更适于飞机电气系统负荷监测和管理。将非侵入式负荷监测方法引入飞机供电系统分析,将为飞机电气管理、故障诊断和预测等进一步研究提供有效参考。     

Infrared radiation simulation of exhaust system by coupling FVM with narrow band k-distribution

A three-dimensional infrared radiation code for exhaust system was developed by the finite volume method coupled with narrow band k-distribution in non-gray absorbing-emitting media. The final infrared signature had considered the atmosphere effect, and the simulation values were favorably consistent with testing ones. The results indicate that the relative errors considering the effect of atmosphere compared with that of the contrary condition reduce by 31%, it shows that when simulating the infrared radiation of the target which is received by the infrared detectors, even the calculation band is in atmospheric windows 3~5 μm, the effect of atmospheric transmission on infrared signature of the target should not be neglected.      

无人机光电载荷地理跟踪控制研究

无人机定点侦察过程中,将地理目标点或图像目标快速锁定在视场内,是十分重要的。在实时定点航迹规划与跟随控制的基础上,提出了光电任务载荷地理跟踪算法,并通过仿真和飞行试验,证明算法可以满足机载平台对地面目标快速锁定的要求。     

基于液晶光阀的动态红外场景仿真研究

介绍了基于液晶光阀的动态红外场景仿真系统构成,分析了液晶光阀的波长变换和空间调制机理。对反映红外场景仿真效果主要因素(光谱输出特性、时间响应特性和空间分辨力)进行了理论分析和研究。利用优化设计液晶光阀参数构建的动态红外场景仿真样机,测量其光谱输出特性、时间响应特性和空间分辨力,结果表明,仿真系统的输出光谱可覆盖中波和长波红外波段,可实现帧频70Hz,系统空间分辨力优于10 lp/mm(受红外光学系统和红外热像仪分辨力限制)。     

无人机载多传感器图像融合评述

为了能为作战指挥系统提供清晰的局部战场信息,提高对局部战场低可观测目标的检测概率、定位精度及识别概率,迫切需要对无人机载SAR、可见光传感器、红外探测器等图像信息及其他非图像信息融合处理。提出了无人机载多传感器图像融合技术需要研究的内容,如: 图像融合新方法研究;无人机载SAR图像的非平稳性处理;基于图像融合目标检测和处理技术; 无人机载图像和非图像信息的融合问题;无人机载多传感器图像融合的实现及评估;多无人机载合成孔径雷达的协同成像;用图像融合的方法实现对运动目标检测等。分析了所提出研究内容的可行性,剖析了其中的关键技术,拟定了可能的技术路线。     

红外导引系统快速原型仿真中的场景生成技术

介绍了基于Vega视景引擎红外场景生成方法,并应用于基于RT—LAB快速原型平台空空导弹红外导引系统快速原型仿真。设计了空空导弹红外导引系统快速原型仿真框架,根据框架建立了弹目6自由度运动学／动力学、红外导引系统Simulink仿真模型及目标等三维几何模型,采用Vega传感器模块和粒子系统模块实现目标各部件温度和干扰弹的自定义设置,同时针对快速原型实时仿真的要求设计了高精度的帧频控制方法。将红外场景生成软件与某空空导弹快速原型仿真系统进行联合仿真进行验证,对空空导弹导引系统的研制与开发起到了重要作用。